Chapter: Reproductive Physiology; Topic: Early Embryonic Development; Subtopic: Transport of Zygote and Role of Zona Pellucida
KEYWORD DEFINITIONS
• Zygote – Fertilized ovum formed after fusion of sperm and oocyte
• Zona pellucida – Glycoprotein layer surrounding early embryo, prevents implantation during transport
• Morula – 16–32 cell stage developing before blastocyst
• Fallopian tube transport – Movement of embryo toward uterus over several days
• Implantation – Embedding of blastocyst into endometrium after shedding zona pellucida
Lead Question – 2016
1. Zygote with zona pellucida reaches uterine cavity by:
A) 2 days
B) 4 days
C) 5 days
D) 6 days
Explanation:
After fertilization in the ampulla of the fallopian tube, the zygote divides to form a morula and moves toward the uterus assisted by ciliary action and smooth muscle contractions. The embryo covered by zona pellucida reaches the uterine cavity around day 4 after fertilization. The zona pellucida prevents premature implantation during tubal transit. Implantation begins only after zona shedding, typically around day 6. Therefore, the correct answer is 4 days. This timing is essential for normal embryonic development.
2. Zona pellucida disappears by which stage?
A) Zygote
B) Morula
C) Early blastocyst
D) Late blastocyst
Explanation:
Zona pellucida is shed during early blastocyst formation to allow implantation into the endometrium. At the morula stage, the embryo still remains surrounded by zona. Zygote also retains zona. Therefore, the correct answer is Early blastocyst. This step, called “hatching,” is essential for implantation readiness.
3. Fertilization usually occurs in:
A) Uterine cavity
B) Cervix
C) Ampulla of fallopian tube
D) Isthmus of fallopian tube
Explanation:
The ampulla of the fallopian tube provides the optimal environment for fertilization due to its wide lumen and presence of cilia. The uterus and cervix are not suitable for fertilization, while the isthmus is too narrow. Thus, the correct answer is Ampulla of fallopian tube. Post-fertilization, the zygote begins cleavage and moves toward the uterus.
4. A patient with damaged fallopian tube cilia is most likely to experience:
A) Early uterine implantation
B) Delayed embryo transport
C) Increased fertility
D) None
Explanation:
Ciliary movement is crucial for proper transport of the zygote. Damage causes delayed transport, increasing the risk of ectopic pregnancy. Early uterine implantation does not occur with delayed movement. Therefore, the correct answer is Delayed embryo transport. This highlights the importance of tubal health in fertility.
5. Implantation typically occurs on which day post-fertilization?
A) Day 2
B) Day 4
C) Day 6–7
D) Day 12
Explanation:
Implantation begins when the blastocyst attaches to the endometrium, typically around day 6–7 after fertilization. Earlier days represent cleavage stages, while day 12 corresponds to deeper placental embedding. Therefore, the correct answer is Day 6–7. Successful implantation requires synchronized endometrial receptivity.
6. Morula typically forms on which day after fertilization?
A) Day 1
B) Day 2
C) Day 3
D) Day 6
Explanation:
The morula forms around day 3 as the zygote undergoes multiple cleavage divisions. It remains surrounded by the zona pellucida until the blastocyst stage. Day 6 corresponds to implantation. Thus, the correct answer is Day 3. The compacted morula then enters the uterine cavity by day 4.
7. Failure of zona hatching causes:
A) Ectopic pregnancy
B) Infertility due to implantation failure
C) Multiple pregnancy
D) Early abortion
Explanation:
If the zona pellucida does not shed, the blastocyst cannot implant into the endometrium, resulting in implantation failure and infertility. Ectopic pregnancy occurs when premature implantation happens in the tube. Therefore, the correct answer is Infertility due to implantation failure. Assisted reproductive techniques sometimes assist hatching.
8. Which hormone prepares endometrium for implantation?
A) FSH
B) LH
C) Estrogen
D) Progesterone
Explanation:
Progesterone transforms the endometrium from proliferative to secretory phase, making it receptive to blastocyst implantation. Estrogen induces proliferation, but progesterone prepares for implantation. FSH and LH regulate ovarian function. Therefore, the correct answer is Progesterone. Adequate progesterone is essential for pregnancy maintenance.
9. A woman with luteal phase defect may experience:
A) Late fertilization
B) Implantation failure
C) Multiple ovulation
D) Increased FSH levels
Explanation:
Luteal phase defect causes insufficient progesterone production, leading to inadequate endometrial receptivity and implantation failure. Fertilization and ovulation remain normal. Thus, the correct answer is Implantation failure. This may present clinically as recurrent early pregnancy loss.
10. Blastocyst contains which two major structures?
A) Trophoblast & inner cell mass
B) Zona pellucida & morula
C) Uterus & cervix
D) Epiblast & hypoblast only
Explanation:
The blastocyst consists of trophoblast cells forming the future placenta and the inner cell mass forming the embryo. Zona exists earlier, not at this stage. Epiblast and hypoblast form later during bilaminar development. Therefore, the correct answer is Trophoblast & inner cell mass. This stage is critical for implantation.
11. Implantation normally occurs at which region of the uterus?
A) Internal os
B) Lower uterine segment
C) Upper posterior wall
D) Cervical canal
Explanation:
Implantation most commonly occurs on the upper posterior uterine wall where blood supply and endometrial thickness are optimal. Implantation at internal os or lower segment is abnormal and leads to placenta previa. Cervical implantation is rare and dangerous. Thus, the correct answer is Upper posterior wall. Proper localization ensures healthy placental development.
Chapter: Physiology – Reproductive Physiology; Topic: Spermatogenesis; Subtopic: Meiotic Events in Sperm Formation
Keyword Definitions:
Spermatogonia: Diploid male germ cells undergoing mitosis before meiosis.
Primary Spermatocyte: Cell entering meiosis I with paired homologous chromosomes.
Independent Assortment: Random segregation of maternal and paternal homologous chromosomes during meiosis I.
Secondary Spermatocyte: Haploid cell after meiosis I containing separated homologs.
Spermatid: Haploid product of meiosis II before morphological maturation.
1) Lead Question – 2016
In spermatogenesis, independent assortment of paternal and maternal chromosomes occurs during–
A) Primary to secondary spermatocyte
B) Spermatogonia to primary spermatocyte
C) Secondary spermatocyte to spermatids
D) Spermatids to spermatozoa
Answer: A) Primary to secondary spermatocyte
Explanation: Independent assortment occurs during meiosis I, specifically in anaphase I when homologous chromosomes separate randomly. In spermatogenesis, this transition corresponds to the change from primary to secondary spermatocyte. Spermatogonia undergo mitosis and therefore cannot show independent assortment. Secondary spermatocytes undergo meiosis II, which only separates sister chromatids without assortment. Spermiogenesis, the conversion of spermatids to spermatozoa, involves morphological changes rather than chromosomal segregation. Thus, the correct answer is A, representing the meiotic step responsible for generating genetic variability in male gametes.
2) Crossing over, which contributes to genetic variability, occurs during–
A) Metaphase I
B) Prophase I
C) Telophase II
D) Interphase
Answer: B) Prophase I
Explanation: Crossing over takes place during prophase I of meiosis when homologous chromosomes undergo synapsis and exchange genetic segments. This increases genetic diversity in gametes. It does not occur during metaphase I, where chromosomes simply align, nor during telophase II, which involves final chromatid separation. Interphase features DNA replication but no chromosomal recombination. In spermatogenesis, this happens within primary spermatocytes. Therefore, B is correct because prophase I is the exclusive stage where recombination occurs, playing a crucial role in creating genetic variation for transmission to future generations.
3) A 25-year-old man with infertility is found to have defective separation of homologous chromosomes during meiosis I. The first affected cell type would be–
A) Spermatogonia
B) Primary spermatocyte
C) Spermatid
D) Spermatozoa
Answer: B) Primary spermatocyte
Explanation: Nondisjunction of homologous chromosomes occurs during meiosis I, which is initiated by primary spermatocytes. Spermatogonia only undergo mitosis and cannot demonstrate meiotic errors. Spermatids are the product of meiosis II and therefore arise after the nondisjunction event, while spermatozoa represent the final differentiated state. Thus, primary spermatocytes are the earliest cells where abnormalities in homolog separation manifest. Therefore, B is the correct answer because these cells directly engage in meiosis I and demonstrate defects leading to aneuploid gametes.
4) The first haploid cells formed during spermatogenesis are–
A) Spermatogonia
B) Primary spermatocytes
C) Secondary spermatocytes
D) Sertoli cells
Answer: C) Secondary spermatocytes
Explanation: Secondary spermatocytes arise after meiosis I, where homologous chromosomes separate, producing haploid cells. Spermatogonia remain diploid and divide mitotically. Primary spermatocytes are also diploid but contain duplicated chromatids. Sertoli cells are supportive somatic cells and not germ cells. Therefore, the first haploid cells in the spermatogenic sequence are secondary spermatocytes. Hence, C is correct because these cells mark the transition from diploidy to haploidy within the meiotic process, representing the successful completion of meiosis I.
5) A 32-year-old male has abnormal sperm with defective acrosome formation. This defect most likely occurred during–
A) Meiosis I
B) Meiosis II
C) Spermiogenesis
D) Spermatogonial mitosis
Answer: C) Spermiogenesis
Explanation: Spermiogenesis transforms spermatids into mature spermatozoa and includes formation of the acrosome, condensation of the nucleus, and development of the flagellum. Meiosis I and II involve chromosomal reduction and separation but not morphological changes. Spermatogonial mitosis is strictly proliferative. Therefore, a defect in acrosome formation specifically implicates spermiogenesis. The correct answer is C because acrosome biogenesis and structural maturation occur exclusively during this phase, essential for oocyte penetration during fertilization.
6) Which cell type contains 46 chromosomes and 92 chromatids?
A) Spermatogonia
B) Primary spermatocyte
C) Secondary spermatocyte
D) Spermatid
Answer: B) Primary spermatocyte
Explanation: Primary spermatocytes arise after DNA replication, possessing 46 chromosomes with duplicated sister chromatids, totaling 92 chromatids, before entering meiosis I. Spermatogonia also contain 46 chromosomes but only 46 chromatids except during S-phase. Secondary spermatocytes and spermatids are haploid with 23 chromosomes. Thus, B is correct because primary spermatocytes uniquely hold the doubled chromatid complement, preparing for meiotic reduction while maintaining diploidy until anaphase I separation.
7) A 29-year-old male with low sperm motility most likely has a defect in–
A) Flagellar axoneme formation
B) Anaphase I separation
C) Spermatogonial mitosis
D) Crossing over
Answer: A) Flagellar axoneme formation
Explanation: Sperm motility depends on a functional flagellum, which contains a 9+2 axoneme structure powered by dynein arms. A defect here directly lowers motility. Anaphase I separation affects chromosomal segregation, not motility. Spermatogonial mitosis impacts germ cell numbers but not movement. Crossing over pertains to genetic recombination rather than motility. Therefore, A is correct because axonemal abnormalities are a primary cause of asthenozoospermia, impairing progressive sperm motility essential for fertility.
8) The immediate product of meiosis II in spermatogenesis is–
A) Spermatogonia
B) Primary spermatocyte
C) Spermatid
D) Sertoli cell
Answer: C) Spermatid
Explanation: Meiosis II separates sister chromatids, producing spermatids, which are haploid cells. Spermatogonia undergo mitosis, not meiosis. Primary spermatocytes enter meiosis I, not II. Sertoli cells are non-dividing supportive cells. Therefore, spermatids are the immediate product of meiosis II. C is correct because these cells represent the earliest stage of haploid germ cells ready to undergo spermiogenesis for final maturation into motile spermatozoa.
9) Nondisjunction of sister chromatids occurs during–
A) Meiosis I
B) Meiosis II
C) Spermiogenesis
D) Interphase
Answer: B) Meiosis II
Explanation: Sister chromatids separate during meiosis II, making nondisjunction at this stage a failure in chromatid segregation. Meiosis I separates homologous chromosomes, not sister chromatids. Spermiogenesis involves structural remodeling, not chromosomal events. Interphase includes DNA replication but no segregation. Thus, B is correct because meiosis II is the phase where chromatids are expected to separate properly, and failures lead to abnormal haploid cells with chromosomal imbalance.
10) A 24-year-old male has impaired Sertoli cell function. Which process is most affected?
A) Blood-testis barrier formation
B) Testosterone synthesis
C) LH secretion
D) Seminal vesicle contraction
Answer: A) Blood-testis barrier formation
Explanation: Sertoli cells create the blood-testis barrier, support germ cells, produce inhibin, and regulate spermatogenesis. They do not synthesize testosterone—that is the role of Leydig cells. LH secretion is regulated by the hypothalamus and pituitary. Seminal vesicle contraction is influenced by the sympathetic nervous system. Therefore, A is correct because Sertoli cells uniquely contribute structural and functional support needed for germ cell protection and maturation.
11) The stage of spermatogenesis involving transformation of haploid cells into mature spermatozoa is–
A) Meiosis I
B) Meiosis II
C) Spermiogenesis
D) Spermatogonial proliferation
Answer: C) Spermiogenesis
Explanation: Spermiogenesis is the process in which spermatids undergo morphological changes including acrosome formation, nuclear condensation, flagellum development, and shedding of excess cytoplasm. Meiosis I and II involve chromosomal reduction and division but not morphologic maturation. Spermatogonial proliferation increases germ cell number but does not contribute to final differentiation. Thus, C is correct because spermiogenesis specifically converts haploid spermatids into fully formed spermatozoa necessary for fertilization.
Chapter: Embryology; Topic: Development of Head and Neck; Subtopic: Embryological Origin of Tongue Muscles
Keyword Definitions:
Occipital Myotomes: Paraxial mesodermal segments migrating to form intrinsic and extrinsic tongue muscles.
Pharyngeal Arches: Embryonic structures contributing to mucosa, cartilage, and skeletal elements of the tongue.
Lateral Plate Mesoderm: Mesoderm forming body wall musculature, not tongue muscles.
Intermediate Mesoderm: Mesoderm responsible for urogenital development.
Hypoglossal Nerve Migration: Nerve accompanying occipital myotomes during tongue muscle development.
1) Lead Question – 2016
Tongue muscles are derived from:
A) Lateral plate mesoderm
B) Occipital myotome
C) Intermediate mesoderm
D) Cervical myotome
Answer: B) Occipital myotome
Explanation: Tongue muscles originate from occipital myotomes, a set of paraxial mesodermal segments that migrate anteriorly along with the hypoglossal nerve. These myogenic precursors give rise to both intrinsic and extrinsic tongue musculature. Lateral plate mesoderm forms limb and body wall muscles, not tongue muscles. Intermediate mesoderm is responsible for kidney and gonadal development. Cervical myotomes do not contribute to tongue formation. Therefore, the correct answer is B, as occipital myotomes are solely responsible for the muscular component of the developing tongue, ensuring coordinated movement essential for swallowing and speech.
2) The epiglottis develops primarily from which pharyngeal arch?
A) First arch
B) Second arch
C) Third arch
D) Fourth arch
Answer: D) Fourth arch
Explanation: The epiglottis arises mainly from the hypobranchial eminence derived predominantly from the fourth pharyngeal arch. The first and second arches form anterior tongue structures, while the third contributes to posterior tongue mucosa. The fourth arch provides material for the epiglottis and laryngeal cartilages. Therefore, the correct answer is D. This structure’s embryological origin explains its innervation pattern and functional association with laryngeal development, particularly its role in protecting the airway during swallowing, contributing to coordinated respiratory and digestive functions.
3) A newborn has paralysis of most tongue muscles. The nerve likely injured is the–
A) Glossopharyngeal nerve
B) Vagus nerve
C) Hypoglossal nerve
D) Facial nerve
Answer: C) Hypoglossal nerve
Explanation: The hypoglossal nerve (CN XII) supplies all intrinsic and extrinsic tongue muscles except palatoglossus. Since these muscles originate from occipital myotomes that migrate with CN XII, damage to this nerve leads to tongue deviation, weak protrusion, and impaired swallowing. The glossopharyngeal nerve mainly provides sensation to the posterior tongue, not motor control. The vagus nerve supplies palatoglossus only. The facial nerve innervates taste buds of the anterior two-thirds but not musculature. Therefore, the correct answer is C, as hypoglossal nerve injury most directly affects tongue muscle function.
4) The mucosa of the anterior two-thirds of the tongue develops from–
A) First pharyngeal arch
B) Second pharyngeal arch
C) Third pharyngeal arch
D) Fourth pharyngeal arch
Answer: A) First pharyngeal arch
Explanation: The anterior two-thirds of the tongue originate from the first pharyngeal arch, specifically from the lateral lingual swellings and tuberculum impar. This region receives general sensation from the mandibular division of the trigeminal nerve. The second arch contributes transiently but regresses. The third arch forms the posterior one-third mucosa, while the fourth arch forms the epiglottic region. Thus, A is correct, reflecting the distinct embryologic segmentation of the tongue crucial for understanding its innervation patterns and clinical correlations involving sensory deficits.
5) A child with impaired swallowing is found to have incomplete tongue muscle development. The embryological defect is most likely in–
A) Occipital somites
B) Cardiac neural crest cells
C) Intermediate mesoderm
D) Sclerotome
Answer: A) Occipital somites
Explanation: Tongue musculature arises from occipital somites, which migrate anteriorly to form intrinsic and extrinsic muscles. A defect here leads to poor motor control affecting swallowing and speech. Cardiac neural crest cells contribute to heart and great vessel development. Intermediate mesoderm forms urogenital organs. Sclerotome produces vertebrae and ribs. Therefore, the correct answer is A. Disruption of occipital somite migration is critical because it directly affects muscular formation and coordination of the tongue, essential for feeding and early speech development.
6) Sensory innervation of the posterior third of the tongue is provided by–
A) Facial nerve
B) Glossopharyngeal nerve
C) Hypoglossal nerve
D) Trigeminal nerve
Answer: B) Glossopharyngeal nerve
Explanation: The posterior third of the tongue originates from the third pharyngeal arch and is supplied by the glossopharyngeal nerve (CN IX). This nerve carries both taste and general sensation from this region. The facial nerve innervates taste buds of the anterior two-thirds. The trigeminal nerve provides general sensation to the anterior tongue. The hypoglossal nerve is motor only. Thus, B is correct, reflecting the embryologic and neuroanatomic foundations of tongue innervation, vital in diagnosing sensory loss and taste abnormalities.
7) A 6-year-old boy presents with difficulty moving his tongue after neck surgery. Which structure was most likely damaged?
A) Lingual nerve
B) External laryngeal nerve
C) Hypoglossal nerve
D) Recurrent laryngeal nerve
Answer: C) Hypoglossal nerve
Explanation: The hypoglossal nerve (CN XII) innervates intrinsic and extrinsic tongue muscles. Damage causes impaired protrusion, deviation toward the injured side, and articulation difficulty. The lingual nerve provides sensation but not motor function. External and recurrent laryngeal nerves supply laryngeal muscles and do not control tongue movement. Therefore, C is correct. This nerve’s proximity to the carotid artery and its course across the neck make it susceptible during surgical procedures, emphasizing its clinical importance in preserving speech and swallowing function.
8) Taste sensation from the anterior two-thirds of the tongue is carried by–
A) Chorda tympani
B) Glossopharyngeal nerve
C) Vagus nerve
D) Hypoglossal nerve
Answer: A) Chorda tympani
Explanation: Taste fibers from the anterior two-thirds of the tongue travel via the chorda tympani branch of the facial nerve. This reflects the transient contribution of the second pharyngeal arch to tongue development. The glossopharyngeal nerve conveys taste from the posterior third. The vagus nerve carries taste from the epiglottis. The hypoglossal nerve supplies motor fibers only. Thus, A is correct. Understanding this distribution is key in evaluating taste disturbances and differentiating sensory deficits due to facial nerve lesions.
9) A newborn with midline tongue cyst likely has a developmental defect in–
A) Tuberculum impar
B) Pharyngeal pouch
C) Intermediate mesoderm
D) Occipital somite
Answer: A) Tuberculum impar
Explanation: The tuberculum impar contributes to the midline portion of the anterior tongue. Abnormal fusion or persistence may lead to midline cysts or lesions. Pharyngeal pouches form glands and do not form tongue tissue. Intermediate mesoderm forms urogenital organs. Occipital somites form tongue muscles, not mucosa. Therefore, A is correct because abnormalities in this early mesenchymal structure cause midline developmental anomalies clinically observed as cysts or masses requiring evaluation.
10) A patient experiences difficulty elevating the tongue. The affected muscle is most likely–
A) Genioglossus
B) Hyoglossus
C) Styloglossus
D) Palatoglossus
Answer: D) Palatoglossus
Explanation: Palatoglossus elevates the posterior tongue and is unique as it is innervated by the vagus nerve via the pharyngeal plexus. Other tongue muscles derive from occipital myotomes and are supplied by the hypoglossal nerve. Genioglossus protrudes, hyoglossus depresses, and styloglossus retracts the tongue. Therefore, D is correct. Understanding these muscles’ embryologic origins and innervations is vital for diagnosing tongue movement disorders and determining whether pathology is muscular or neural in origin.
11) Failure of migration of occipital myotomes during development would primarily affect–
A) Tongue musculature
B) Pharyngeal arch skeleton
C) Parathyroid glands
D) Thyroid cartilage
Answer: A) Tongue musculature
Explanation: Occipital myotomes migrate anteriorly with the hypoglossal nerve to form intrinsic and extrinsic tongue muscles. A failure in this migration impairs muscle formation, resulting in defective movement, poor feeding, and impaired speech development. Pharyngeal arch skeleton and thyroid cartilage arise from neural crest cells. Parathyroid glands originate from third and fourth pharyngeal pouches. Therefore, A is correct because the muscular component of the tongue depends solely on successful occipital myotome migration during embryogenesis.
Chapter: Embryology; Topic: Fetal Circulation & Umbilical Structures; Subtopic: Derivatives of Umbilical Arteries
Keyword Definitions:
Umbilical Arteries: Fetal vessels carrying deoxygenated blood to the placenta.
Distal Umbilical Artery: Portion that degenerates after birth forming a fibrous ligament.
Medial Umbilical Ligament: Fibrous remnant of the distal parts of umbilical arteries.
Superior Vesical Artery: Patent proximal part of umbilical arteries supplying the bladder.
Ligamentum Teres: Remnant of the left umbilical vein, not the artery.
1) Lead Question – 2016
Which of the following is remnant of distal umbilical artery?
A) Ligamentum Teres
B) Superior Vesical artery
C) Medial umbilical Ligament
D) Ligamentum arteriosum
Answer: C) Medial umbilical ligament
Explanation: After birth, the distal part of the umbilical artery fibroses and becomes the medial umbilical ligament. The proximal part remains patent as the superior vesical artery supplying the bladder. Ligamentum teres is derived from the left umbilical vein, while the ligamentum arteriosum is a remnant of the ductus arteriosus. Thus, the correct answer is C. The medial umbilical ligament runs on the internal surface of the anterior abdominal wall and is clinically significant because it forms an important landmark during pelvic surgery and laparoscopic procedures.
2) The proximal part of the umbilical artery in adults forms the–
A) Inferior epigastric artery
B) Superior vesical artery
C) Obturator artery
D) Deep circumflex artery
Answer: B) Superior vesical artery
Explanation: The proximal portion of the umbilical artery remains functional after birth and forms the superior vesical artery, which supplies the upper part of the urinary bladder. Other listed arteries have different embryological origins and are not derived from umbilical vessels. Thus, B is correct. This persistence reflects the fetal requirement for bladder blood supply continuing after birth, while the distal segment, no longer required for placental circulation, becomes fibrotic, forming the medial umbilical ligament.
3) A newborn undergoes surgery for bladder exstrophy. During the procedure, surgeons identify fibrous bands extending from the bladder to the abdominal wall. These are most likely–
A) Lateral umbilical folds
B) Medial umbilical ligaments
C) Round ligament of liver
D) Falx inguinalis
Answer: B) Medial umbilical ligaments
Explanation: Medial umbilical ligaments are remnants of the distal umbilical arteries and lie on the internal surface of the anterior abdominal wall. In bladder exstrophy, these structures are often visible surgically. Lateral umbilical folds contain inferior epigastric vessels. The round ligament of the liver is a remnant of the umbilical vein. Falx inguinalis is part of the conjoint tendon. Thus, B is correct because these ligaments represent the embryologic remains directly associated with bladder development and anterior abdominal wall anatomy.
4) Which of the following is derived from the left umbilical vein?
A) Medial umbilical ligament
B) Ligamentum venosum
C) Ligamentum teres hepatis
D) Ligamentum arteriosum
Answer: C) Ligamentum teres hepatis
Explanation: The left umbilical vein becomes the ligamentum teres hepatis after birth as placental circulation ceases. The medial umbilical ligament is derived from the distal umbilical artery, and the ligamentum arteriosum from the ductus arteriosus. The ligamentum venosum originates from the ductus venosus. Thus, C is correct. This structure runs along the free margin of the falciform ligament and is important surgically as a landmark separating the anatomical lobes of the liver.
5) A 3-day-old neonate shows absent closure of the distal umbilical arteries. This condition may present with–
A) Persistent abdominal wall pulsations
B) Umbilical granuloma
C) Patent urachus
D) Failure of ductus venosus closure
Answer: A) Persistent abdominal wall pulsations
Explanation: Failure of the distal umbilical arteries to fibrose may lead to persistent pulsatile vessels near the umbilicus. Umbilical granuloma results from incomplete epithelialization. Patent urachus connects bladder and umbilicus and involves urachal remnants, not arteries. Closure of the ductus venosus is unrelated. Thus, A is correct, reflecting the persistence of vascular flow in fetal arteries that normally become medial umbilical ligaments.
6) The ductus arteriosus becomes which adult structure?
A) Ligamentum venosum
B) Ligamentum teres
C) Ligamentum arteriosum
D) Medial umbilical ligament
Answer: C) Ligamentum arteriosum
Explanation: The ductus arteriosus, which shunts blood from the pulmonary trunk to the aorta during fetal life, closes after birth to form the ligamentum arteriosum. Ligamentum venosum derives from ductus venosus, ligamentum teres from the umbilical vein, and the medial umbilical ligament from distal umbilical arteries. Thus, C is correct. This structure is clinically significant because the left recurrent laryngeal nerve loops beneath it, making it important in thoracic surgical anatomy.
7) A newborn has a patent ductus arteriosus. This fetal vessel normally connects the–
A) Aorta to inferior vena cava
B) Pulmonary artery to aorta
C) Pulmonary vein to left atrium
D) SVC to right atrium
Answer: B) Pulmonary artery to aorta
Explanation: The ductus arteriosus diverts blood from the pulmonary trunk directly to the aorta, bypassing the non-functioning fetal lungs. After birth, increased oxygen tension induces closure. A patent ductus leads to a left-to-right shunt and continuous murmur. Other options do not represent fetal shunts. Thus, B is correct. Understanding fetal circulation helps clinicians diagnose congenital heart anomalies and manage neonatal cardiovascular conditions effectively.
8) The urachus in adults becomes the–
A) Medial umbilical ligament
B) Round ligament
C) Median umbilical ligament
D) Lateral umbilical fold
Answer: C) Median umbilical ligament
Explanation: The median umbilical ligament is the fibrotic remnant of the urachus, a fetal connection between the bladder and umbilicus. Medial umbilical ligaments arise from distal umbilical arteries, lateral umbilical folds contain inferior epigastric vessels, and the round ligament represents the umbilical vein. Thus, C is correct. A persistent urachus may produce urine discharge from the umbilicus, requiring surgical correction.
9) Which fetal structure allows oxygenated blood from the placenta to bypass the liver?
A) Ductus arteriosus
B) Ductus venosus
C) Foramen ovale
D) Umbilical artery
Answer: B) Ductus venosus
Explanation: The ductus venosus channels oxygen-rich blood from the umbilical vein directly into the IVC, bypassing hepatic circulation. The ductus arteriosus bypasses the lungs, and the foramen ovale shunts blood between atria. The umbilical artery carries deoxygenated blood. Thus, B is correct. Closure of this structure after birth forms the ligamentum venosum, important in hepatic surgical anatomy.
10) A surgeon tracing the medial umbilical ligament notes its course toward the–
A) Umbilicus
B) Liver
C) Renal hilum
D) Lumbar vertebrae
Answer: A) Umbilicus
Explanation: The medial umbilical ligament courses superiorly on the posterior surface of the anterior abdominal wall toward the umbilicus. It marks the obliterated distal umbilical artery. It does not extend toward the liver (round ligament), renal hilum, or lumbar vertebrae. Thus, A is correct. These ligaments create identifiable folds important in laparoscopic hernia repair, serving as landmarks that help differentiate direct and indirect inguinal hernias.
11) A neonate with umbilical discharge containing urine likely has a defect involving the–
A) Medial umbilical ligament
B) Urachus
C) Umbilical vein
D) Ductus arteriosus
Answer: B) Urachus
Explanation: A patent urachus causes urine leakage from the umbilicus, resulting from failure of the allantoic duct to close. The medial umbilical ligament forms from umbilical artery remnants and is unrelated. The umbilical vein becomes the ligamentum teres, while the ductus arteriosus forms the ligamentum arteriosum. Thus, B is correct. Recognizing clinical signs helps differentiate urachal anomalies from other umbilical pathologies, ensuring proper surgical intervention.
Chapter: Embryology; Topic: Neural Crest Cell Derivatives; Subtopic: Structures Arising From Neural Crest
Keyword Definitions:
Neural Crest Cells: Migratory embryonic cells giving rise to diverse tissues including ganglia and pigment cells.
Adrenal Medulla: Inner part of adrenal gland derived from neural crest chromaffin cells.
Pigment Cells (Melanocytes): Neural crest–derived cells producing melanin.
Corneal Stroma: Mesenchymal tissue derived largely from neural crest migration.
Retinal Pigmented Epithelium (RPE): Derived from neuroectoderm of optic cup, not neural crest.
1) Lead Question – 2016
All are derived from neural crest except?
A) Adrenal medulla
B) Pigment cell in skin
C) Corneal stroma
D) Retinal pigmented epithelium
Answer: D) Retinal pigmented epithelium
Explanation: Neural crest cells give rise to multiple structures including adrenal medulla, melanocytes, corneal stroma, craniofacial cartilage, and Schwann cells. The retinal pigmented epithelium (RPE), however, develops from the outer layer of the optic cup, which is derived from neuroectoderm, not neural crest. Thus, D is correct. Understanding this distinction helps differentiate between neuroectodermal and neural crest derivatives, particularly in congenital malformations affecting the eye, adrenal glands, or craniofacial structures. Neural crest migration is key to forming peripheral nervous system components and pigmentation patterns.
2) Which of the following is derived from neural crest cells?
A) Dorsal root ganglia
B) Anterior pituitary
C) Optic nerve
D) Lens
Answer: A) Dorsal root ganglia
Explanation: Neural crest cells form the dorsal root ganglia, autonomic ganglia, melanocytes, and Schwann cells. The anterior pituitary originates from oral ectoderm (Rathke’s pouch), the lens from surface ectoderm, and the optic nerve from neuroectoderm. Thus, A is correct. This distinction is clinically significant because neural crest defects can affect sensory and autonomic ganglia, presenting with neurological and pigmentation abnormalities in congenital syndromes such as Hirschsprung disease and Waardenburg syndrome.
3) A newborn presents with congenital absence of enteric ganglia in the colon. The embryological defect involves–
A) Neural crest migration
B) Neural tube closure
C) Endoderm differentiation
D) Mesoderm segmentation
Answer: A) Neural crest migration
Explanation: Hirschsprung disease results from failed migration of neural crest cells into the distal colon, leading to absence of enteric ganglia. Neural tube closure defects cause neural tube anomalies such as spina bifida. Endoderm forms gut epithelium and mesoderm forms muscle and connective tissue. Thus, A is correct. Neural crest migration defects lead to aganglionosis, impaired peristalsis, and colonic dilation, essential concepts for diagnosing congenital gastrointestinal motility disorders.
4) Melanocytes are derived from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest cells
D) Endoderm
Answer: C) Neural crest cells
Explanation: Melanocytes originate from neural crest cells that migrate into the epidermis. Surface ectoderm forms epidermal keratinocytes, endoderm forms internal organ epithelium, and mesoderm forms connective tissues and muscles. Therefore, C is correct. Defects in melanocyte migration or function lead to disorders such as albinism and piebaldism, demonstrating their critical role in pigmentation and dermatologic development.
5) A child with suspected neurofibromatosis has multiple nerve sheath tumors. These tumors arise from cells derived from–
A) Astrocytes
B) Neural crest
C) Endoderm
D) Somitomeres
Answer: B) Neural crest
Explanation: Schwann cells, which form the basis of neurofibromas, are neural crest derivatives. Astrocytes derive from neuroectoderm, endoderm forms internal lining tissues, and somitomeres form skeletal muscle. Thus, B is correct. Neurofibromatosis features neural crest-derived tumors involving Schwann cells, emphasizing the diverse lineage and clinical importance of neural crest derivatives in peripheral nerve pathology.
6) Which of the following structures is not neural crest derived?
A) Schwann cells
B) Chromaffin cells
C) Parafollicular cells of thyroid
D) Retina
Answer: D) Retina
Explanation: The retina arises from neuroectoderm of the optic cup. Schwann cells, chromaffin cells of adrenal medulla, and parafollicular cells (C cells) of the thyroid are neural crest derivatives. Therefore, D is correct. Retinal development is tightly linked to optic vesicle formation, distinctly separate from migratory neural crest pathways that contribute to endocrine and peripheral nervous system structures.
7) A neonate presents with hypocalcemia and thymic aplasia. The embryological defect most likely involves–
A) Third pharyngeal pouch
B) Fourth pharyngeal pouch
C) Neural crest cells
D) Surface ectoderm
Answer: A) Third pharyngeal pouch
Explanation: DiGeorge syndrome involves maldevelopment of the third and fourth pharyngeal pouches, with the third giving rise to thymus and inferior parathyroids. Neural crest defects also contribute but the primary pouch abnormality is key. Surface ectoderm does not form these structures. Thus, A is correct. The syndrome results in T-cell deficiency and hypocalcemia due to thymic and parathyroid defects respectively.
8) Parafollicular (C) cells of the thyroid originate from–
A) Endoderm
B) Mesoderm
C) Neural crest
D) Surface ectoderm
Answer: C) Neural crest
Explanation: C cells derive from neural crest cells associated with the ultimobranchial body, which fuses with the thyroid. Endoderm forms thyroid follicles, mesoderm does not contribute, and surface ectoderm forms skin derivatives. Thus, C is correct. These cells secrete calcitonin and are involved in medullary thyroid carcinoma, emphasizing their clinical and embryological relevance.
9) Which of the following is derived from neuroectoderm rather than neural crest?
A) Retina
B) Odontoblasts
C) Melanocytes
D) Meninges (arachnoid/pia)
Answer: A) Retina
Explanation: The retina develops from the optic cup, a neuroectodermal derivative. Odontoblasts, melanocytes, and the pia-arachnoid mater arise from neural crest. Thus, A is correct. This distinction is crucial in ophthalmic embryology, explaining why retinal diseases reflect neural tissue behavior rather than neural crest–derived supportive structures.
10) A child presents with congenital absence of sympathetic ganglia. This defect involves failure of development of–
A) Neural tube
B) Neural crest cells
C) Somatic mesoderm
D) Intermediate mesoderm
Answer: B) Neural crest cells
Explanation: Sympathetic ganglia arise from migrating neural crest cells forming the autonomic nervous system. Neural tube forms CNS structures, somatic mesoderm produces body wall muscles, and intermediate mesoderm forms urogenital organs. Thus, B is correct. Such defects manifest clinically as autonomic dysfunction, emphasizing the importance of neural crest migration in forming the sympathetic chain.
11) Corneal endothelium and stroma arise mainly from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest cells
D) Endoderm
Answer: C) Neural crest cells
Explanation: Neural crest cells migrate into the developing eye contributing to corneal stroma and endothelium. Surface ectoderm forms the lens and corneal epithelium, mesoderm contributes minimally to ocular structures, and endoderm plays no role. Thus, C is correct. Disorders of neural crest migration can result in anterior segment dysgenesis such as Axenfeld–Rieger anomaly.
Chapter: Embryology; Topic: Development of Eye; Subtopic: Derivatives of Optic Vesicle
Keyword Definitions:
Optic Vesicle: Lateral outgrowth from forebrain neuroectoderm forming major ocular structures.
Neuroectoderm: Embryonic tissue giving rise to retina, optic nerve, and optic stalk.
Surface Ectoderm: Forms lens, corneal epithelium, and eyelid structures.
Mesoderm: Contributes to extraocular muscles and some vascular components.
Neural Crest Cells: Form corneal stroma, sclera, and choroid.
1) Lead Question – 2016
Optic vesicle is derived from–
A) Endoderm
B) Mesoderm
C) Neuroectoderm
D) Surface ectoderm
Answer: C) Neuroectoderm
Explanation: The optic vesicle develops as a lateral evagination of the forebrain neuroectoderm. It later forms the optic cup, which gives rise to the neural and pigmented layers of the retina. Surface ectoderm forms the lens, while mesoderm contributes to vascular and muscular structures around the eye. Endoderm does not participate in ocular formation. Therefore, the correct answer is C. Neuroectodermal origin explains the similarity between the retina and central nervous system tissues and underlies ocular disorders linked to neural developmental defects.
2) The lens of the eye is derived from–
A) Neuroectoderm
B) Surface ectoderm
C) Mesoderm
D) Endoderm
Answer: B) Surface ectoderm
Explanation: The lens originates from surface ectoderm after induction by the underlying optic vesicle. Neuroectoderm forms the retina and optic nerve, mesoderm contributes vascular tissues, and endoderm plays no role in eye formation. Thus, B is correct. This developmental interaction highlights the importance of inductive signaling between neural and ectodermal tissues, essential for normal lens development and preventing congenital anomalies such as aphakia.
3) A newborn presents with congenital absence of the retina. The embryological defect most likely involves failure of development of the–
A) Optic cup
B) Lens placode
C) Mesoderm
D) Neural crest cells
Answer: A) Optic cup
Explanation: The optic cup is derived from neuroectoderm and forms both layers of the retina. Failure of its development leads to retinal agenesis. Lens placode generates the lens, mesoderm contributes extraocular muscles, and neural crest forms corneal stroma and sclera. Thus, A is correct. Understanding this helps clinicians evaluate ocular malformations and recognize primary defects in neural tissue rather than accessory ocular structures.
4) The corneal epithelium is derived from–
A) Surface ectoderm
B) Mesoderm
C) Neural crest
D) Neuroectoderm
Answer: A) Surface ectoderm
Explanation: The corneal epithelium forms from surface ectoderm, similar to the lens and conjunctiva. Mesoderm does not form epithelium, neural crest forms corneal stroma and endothelium, and neuroectoderm forms retina. Thus, A is correct. This explains why corneal epithelial disorders behave like ectodermal defects and differ from stromal conditions involving neural crest abnormalities.
5) A child presents with hypoplasia of the optic nerve. This structure is derived from–
A) Surface ectoderm
B) Mesoderm
C) Neuroectoderm
D) Endoderm
Answer: C) Neuroectoderm
Explanation: The optic nerve arises from axons of retinal ganglion cells, which originate from neuroectoderm. Mesoderm forms surrounding connective tissues, surface ectoderm forms the lens, and endoderm does not contribute to ocular structures. Thus, C is correct. Optic nerve defects therefore reflect central nervous system–related developmental anomalies rather than surface or mesodermal abnormalities.
6) The choroid and sclera primarily develop from–
A) Neural crest cells
B) Surface ectoderm
C) Endoderm
D) Neuroectoderm
Answer: A) Neural crest cells
Explanation: Neural crest contributes extensively to connective tissue structures of the eye including sclera, choroid, and corneal stroma. Neuroectoderm forms retina and optic nerve, surface ectoderm forms lens and corneal epithelium, and endoderm has no ocular role. Thus, A is correct. Maldevelopment of neural crest leads to anterior segment dysgenesis, highlighting the importance of these migratory cells.
7) A neonate with aniridia likely has a defect in development of the–
A) Optic vesicle
B) Surface ectoderm
C) Neural crest migration
D) Mesodermal condensation
Answer: A) Optic vesicle
Explanation: The iris stroma and muscles originate from the optic cup, an extension of the optic vesicle. Deficiency in its development can cause aniridia. Neural crest forms supporting stromal tissues but not the iris muscles themselves. Surface ectoderm forms lens, not iris, and mesoderm contributes minimally. Thus, A is correct. Aniridia often accompanies PAX6 gene defects, demonstrating the close linkage between optic vesicle development and ocular patterning.
8) The retinal pigment epithelium develops from–
A) Neural crest
B) Surface ectoderm
C) Neuroectoderm
D) Mesoderm
Answer: C) Neuroectoderm
Explanation: The RPE forms from the outer layer of the optic cup derived from neuroectoderm. Neural crest forms corneal stroma and sclera, surface ectoderm forms lens epithelium, and mesoderm supports vascular components. Thus, C is correct. RPE disorders reflect intrinsic neural developmental abnormalities rather than neural crest–related defects.
9) A congenital coloboma results from failure of closure of the–
A) Optic fissure
B) Lens pit
C) Corneal groove
D) Vitreous cavity
Answer: A) Optic fissure
Explanation: Coloboma is caused by incomplete closure of the embryonic optic fissure, a neuroectodermal defect. Lens pit abnormalities cause aphakia, corneal groove issues cause anterior chamber defects, and vitreous cavity malformations cause posterior eye abnormalities. Thus, A is correct. Colobomas can affect iris, choroid, retina, or optic nerve depending on the extent of fissure persistence.
10) The extraocular muscles arise from–
A) Neural crest cells
B) Preotic mesoderm
C) Surface ectoderm
D) Neuroectoderm
Answer: B) Preotic mesoderm
Explanation: Extraocular muscles develop from preotic mesodermal myotomes. Neural crest contributes to connective tissue coverings, surface ectoderm forms lens and cornea, and neuroectoderm forms retina and optic nerve. Thus, B is correct. These structures are essential for coordinated eye movements and their embryologic origin explains their distinct innervation by cranial nerves III, IV, and VI.
11) A baby has congenital cataract due to defective development of the–
A) Lens placode
B) Optic cup
C) Neural crest
D) Mesoderm
Answer: A) Lens placode
Explanation: The lens placode, derived from surface ectoderm, forms the lens. Defects produce congenital cataracts. Optic cup abnormalities affect retina, neural crest affects corneal stroma and sclera, and mesoderm contributes vascular tissues. Thus, A is correct. Cataract formation underscores the critical inductive interactions between optic vesicle and surface ectoderm in lens morphogenesis.
Chapter: Embryology; Topic: Pharyngeal Apparatus; Subtopic: Third & Fourth Pharyngeal Pouch Anomalies – DiGeorge Syndrome
Keyword Definitions:
Pharyngeal Pouches: Endoderm-lined sacs giving rise to thymus, parathyroids, and other neck structures.
DiGeorge Syndrome: Developmental disorder due to failure of third and fourth pouch formation.
Thymic Hypoplasia: Underdeveloped thymus leading to T-cell immunodeficiency.
Hypocalcemia: Low calcium from absent/inadequate parathyroid glands.
22q11 Deletion: Chromosomal microdeletion associated with DiGeorge syndrome.
1) Lead Question – 2016
DiGeorge syndrome is characterized by all except?
A) Congenital thymic hypoplasia
B) Abnormal development of third and fourth pouches
C) Hypothyroidism
D) Hypocalcemic tetany
Answer: C) Hypothyroidism
Explanation: DiGeorge syndrome results from defective development of the third and fourth pharyngeal pouches, causing thymic hypoplasia and absent or hypoplastic parathyroid glands. This leads to T-cell immunodeficiency and hypocalcemic tetany. Hypothyroidism is not a typical feature because the thyroid gland develops from a midline endodermal diverticulum, not from the pharyngeal pouches affected in DiGeorge syndrome. Therefore, the correct answer is C. Understanding pouch derivatives helps identify associated clinical defects including immune deficiency, hypocalcemia, cardiac anomalies, and craniofacial abnormalities.
2) The thymus primarily develops from which pharyngeal pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: C) Third
Explanation: The thymus arises from the ventral wing of the third pharyngeal pouch, which also contributes to the inferior parathyroid glands. The first pouch forms the middle ear and auditory tube, while the second forms tonsillar epithelium. The fourth pouch forms superior parathyroids. Thus, C is correct. Failure of the third pouch produces thymic hypoplasia seen in DiGeorge syndrome, resulting in T-cell immunodeficiency and recurrent infections.
3) A newborn with DiGeorge syndrome is most likely to have which endocrine abnormality?
A) Hyperparathyroidism
B) Hypocalcemia
C) Cortisol deficiency
D) Hyperthyroidism
Answer: B) Hypocalcemia
Explanation: Hypocalcemia arises due to absent or hypoplastic parathyroid glands derived from the third and fourth pharyngeal pouches. Hyperparathyroidism does not occur because the glands are underdeveloped. Cortisol deficiency involves adrenal defects, unrelated to pharyngeal pouches. Thyroid disorders are not typical in DiGeorge syndrome. Thus, B is correct. The resulting low calcium levels can cause tetany or seizures in neonates, making recognition clinically important.
4) Which cardiac defect is frequently associated with DiGeorge syndrome?
A) Atrial septal defect
B) Tetralogy of Fallot
C) Patent ductus arteriosus
D) Coarctation of aorta
Answer: B) Tetralogy of Fallot
Explanation: DiGeorge syndrome often presents with conotruncal cardiac anomalies such as tetralogy of Fallot, truncus arteriosus, and interrupted aortic arch. These arise from abnormal neural crest cell migration affecting outflow tract development. ASD and PDA occur in many conditions but are not characteristic associations. Thus, B is correct. Defective neural crest development ties together cardiac, craniofacial, and thymic abnormalities seen clinically.
5) The inferior parathyroid glands develop from which pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: C) Third
Explanation: The third pharyngeal pouch gives rise to the thymus (ventral wing) and inferior parathyroid glands (dorsal wing). The fourth pouch gives rise to the superior parathyroids. The first and second pouches form ear and tonsillar structures. Thus, C is correct. DiGeorge syndrome involving failed development of the third pouch therefore produces hypocalcemia due to missing inferior parathyroids.
6) A child with recurrent viral infections and absent T-cells likely has underdevelopment of–
A) Parathyroid glands
B) Thymus
C) Thyroid gland
D) Adrenal cortex
Answer: B) Thymus
Explanation: The thymus is essential for T-cell maturation. In DiGeorge syndrome, thymic hypoplasia leads to profound T-cell deficiency, causing recurrent viral and fungal infections. Parathyroid defects cause hypocalcemia, not immune deficiency. Thyroid and adrenal cortex do not significantly influence T-cell maturation. Thus, B is correct. Thymic aplasia is a hallmark feature of third pouch developmental disorders.
7) The superior parathyroid glands are derivatives of which pouch?
A) First
B) Second
C) Third
D) Fourth
Answer: D) Fourth
Explanation: The superior parathyroids arise from the dorsal wing of the fourth pharyngeal pouch, while the inferior parathyroids develop from the third. This positional reversal reflects migration patterns. The first pouch forms auditory structures and the second forms tonsillar tissues. Thus, D is correct. Defects in fourth pouch development contribute to hypocalcemia seen in DiGeorge syndrome.
8) A patient with DiGeorge syndrome may present with which craniofacial feature?
A) Macroglossia
B) Cleft palate
C) Microtia
D) Hemifacial microsomia
Answer: B) Cleft palate
Explanation: Cleft palate commonly occurs in DiGeorge syndrome due to defective neural crest migration affecting facial development. Macroglossia is seen in Beckwith–Wiedemann syndrome; microtia in first arch defects; hemifacial microsomia in Goldenhar syndrome. Thus, B is correct. Craniofacial abnormalities often accompany immune and cardiac defects in this condition, reflecting shared developmental pathways.
9) Hypocalcemic tetany in DiGeorge syndrome is due to absence of–
A) Superior parathyroids
B) Inferior parathyroids
C) Both superior and inferior parathyroids
D) Thyroid follicular cells
Answer: C) Both superior and inferior parathyroids
Explanation: Although classically associated with inferior parathyroid agenesis, DiGeorge syndrome may involve defective development of both third and fourth pouches, causing loss of both sets of parathyroids. Thyroid follicular cells arise from endoderm and are unaffected. Thus, C is correct. Severe hypocalcemia can manifest as muscle spasms, laryngospasm, or seizures, requiring prompt correction.
10) Which chromosomal deletion is most commonly associated with DiGeorge syndrome?
A) 7q11 deletion
B) 22q11 deletion
C) 5p deletion
D) 15q11 deletion
Answer: B) 22q11 deletion
Explanation: The 22q11 microdeletion disrupts TBX1 gene expression, impairing neural crest migration and pharyngeal pouch development. 7q11 deletion causes Williams syndrome; 5p deletion causes Cri-du-chat; 15q11 abnormalities involve Prader–Willi and Angelman syndromes. Thus, B is correct. The 22q11 deletion explains the multi-system presentation of DiGeorge syndrome, including cardiac, immune, facial, and endocrine abnormalities.
11) A neonate with DiGeorge syndrome is most likely to show–
A) Elevated T-cell count
B) Low serum calcium
C) Elevated thyroid hormones
D) High cortisol
Answer: B) Low serum calcium
Explanation: Low serum calcium reflects absent or hypoplastic parathyroid glands derived from third and fourth pharyngeal pouches. T-cells are typically reduced, not elevated. Thyroid and adrenal hormones are generally normal. Thus, B is correct. Early recognition of hypocalcemia is critical as it may present with tetany or seizures in affected neonates.
Chapter: Embryology; Topic: Development of Brain; Subtopic: Formation of Commissural Structures
Keyword Definitions:
Lamina Terminalis: Region at the rostral end of neural tube from which commissures, including corpus callosum, develop.
Corpus Callosum: Largest commissural fiber bundle connecting cerebral hemispheres.
Basal Plate: Ventral neural tube region forming motor nuclei.
Alar Plate: Dorsal neural tube region forming sensory nuclei.
Commissures: Fiber tracts connecting corresponding cortical areas across hemispheres.
1) Lead Question – 2016
Part of neural tube from which corpus callosum develops:
A) Basal lamina
B) Alar lamina
C) Lamina terminalis
D) Basal plate
Answer: C) Lamina terminalis
Explanation: The corpus callosum develops from the lamina terminalis, located at the rostral end of the neural tube. It forms the major commissural pathway connecting the cerebral hemispheres. The basal plate gives rise to motor nuclei, and the alar plate forms sensory nuclei, neither contributing to commissural fiber formation. The lamina terminalis serves as the primitive anterior wall of the third ventricle and is crucial for the formation of major forebrain commissures. Therefore, C is correct, reflecting the specific origin of interhemispheric connectivity in brain development.
2) The anterior commissure develops from the region near the–
A) Lamina terminalis
B) Basal plate
C) Alar plate
D) Pontine flexure
Answer: A) Lamina terminalis
Explanation: The anterior commissure, like the corpus callosum, forms in association with the lamina terminalis at the rostral neural tube. Basal and alar plates form motor and sensory nuclei, respectively, and the pontine flexure contributes to hindbrain shaping. Thus, A is correct. This commissure connects olfactory structures and parts of the temporal lobes, highlighting the lamina terminalis as the central site for forebrain commissural formation.
3) A newborn with agenesis of corpus callosum most likely has a developmental defect in the–
A) Lamina terminalis
B) Neural crest
C) Basal plate
D) Otic placode
Answer: A) Lamina terminalis
Explanation: Agenesis of the corpus callosum results from failed development of commissural fibers across the lamina terminalis. Neural crest defects produce craniofacial and autonomic abnormalities, whereas basal plate defects affect motor nuclei, and otic placode forms the inner ear. Thus, A is correct. Absence of interhemispheric fibers may lead to developmental delays, seizures, or be asymptomatic depending on compensatory pathways.
4) The basal plate gives rise to–
A) Motor nuclei
B) Sensory nuclei
C) Commissural fibers
D) Cerebellar cortex
Answer: A) Motor nuclei
Explanation: The basal plate of the neural tube forms motor neurons and motor cranial nerve nuclei. Sensory nuclei arise from the alar plate, commissural fibers from the lamina terminalis, and cerebellar cortex from the rhombic lip. Thus, A is correct. This organization explains the ventral motor and dorsal sensory arrangement of the spinal cord and brainstem, essential for neuroanatomical localization.
5) A child with defective sensory nuclei formation likely has an abnormality in the–
A) Alar plate
B) Basal lamina
C) Mesoderm
D) Hypothalamus
Answer: A) Alar plate
Explanation: The alar plate forms sensory nuclei in the spinal cord and brainstem. Basal plate forms motor structures, mesoderm forms connective and muscular tissues, and hypothalamus develops from diencephalic neuroectoderm. Thus, A is correct. Defects lead to impaired sensory processing and clinical symptoms such as reduced pain, touch, or proprioceptive abilities.
6) Which structure is derived from the diencephalon?
A) Thalamus
B) Pons
C) Cerebellum
D) Medulla
Answer: A) Thalamus
Explanation: The thalamus arises from the diencephalon, which also forms hypothalamus and epithalamus. Pons and medulla derive from hindbrain (metencephalon and myelencephalon), and cerebellum from the rhombic lip. Thus, A is correct. The diencephalon’s development is important for sensory relay and autonomic regulation, central to neurological function.
7) A newborn with holoprosencephaly likely has defective development of the–
A) Prosencephalon
B) Metencephalon
C) Myelencephalon
D) Neural crest
Answer: A) Prosencephalon
Explanation: Holoprosencephaly results from failure of prosencephalon to divide into two hemispheres. Metencephalon forms pons and cerebellum; myelencephalon forms medulla; neural crest forms peripheral structures. Thus, A is correct. This condition ranges from mild midline defects to severe craniofacial abnormalities, often associated with genetic and environmental factors.
8) The pineal gland develops from–
A) Telencephalon
B) Diencephalon
C) Mesencephalon
D) Neural crest
Answer: B) Diencephalon
Explanation: The pineal gland arises from the roof of the diencephalon, alongside structures such as the epithalamus. Telencephalon forms cerebral hemispheres, mesencephalon forms midbrain, and neural crest forms connective tissues and ganglia. Thus, B is correct. The pineal gland regulates melatonin secretion and circadian rhythms, demonstrating its neuroendocrine role.
9) Posterior pituitary gland originates from–
A) Rathke’s pouch
B) Infundibulum
C) Neural crest
D) Surface ectoderm
Answer: B) Infundibulum
Explanation: The posterior pituitary (neurohypophysis) forms from neuroectoderm of the diencephalic infundibulum. Rathke’s pouch forms the anterior pituitary. Neural crest and surface ectoderm do not form these structures. Thus, B is correct. This explains how posterior pituitary stores and releases hypothalamic hormones such as ADH and oxytocin.
10) A neonate has facial anomalies and outflow tract defects. The embryological cause likely involves–
A) Neural crest migration
B) Lamina terminalis
C) Rathke’s pouch
D) Notochord
Answer: A) Neural crest migration
Explanation: Neural crest cells contribute to craniofacial structures and cardiac outflow tracts. Defects cause syndromes like DiGeorge and craniofacial dysostosis. Lamina terminalis forms commissures, Rathke’s pouch forms anterior pituitary, and notochord induces neural tube but does not form these structures. Thus, A is correct. Migration failures result in combined craniofacial and cardiac anomalies.
11) The cerebral hemispheres arise from the–
A) Telencephalon
B) Diencephalon
C) Mesencephalon
D) Myelencephalon
Answer: A) Telencephalon
Explanation: The telencephalon forms cerebral hemispheres, basal ganglia, and olfactory bulbs. Diencephalon forms thalamus and hypothalamus, mesencephalon forms midbrain, and myelencephalon forms medulla. Thus, A is correct. Proper development is essential for cognition, coordination, and higher neurological functions.
Chapter: Histology; Topic: Urinary System; Subtopic: Epithelial Lining of Urinary Tract
Keyword Definitions:
Transitional Epithelium (Urothelium): Stratified epithelium specialized for stretch, lines renal pelvis to proximal urethra.
Dome Cells: Superficial umbrella cells characteristic of bladder epithelium.
Stratified Squamous Epithelium: Protective epithelium seen in distal urethra.
Cuboidal Epithelium: Single-layered epithelium seen in ducts and tubules, not bladder.
Columnar Epithelium: Tall cells lining absorptive or secretory surfaces, not bladder.
1) Lead Question – 2016
Epithelial lining of urinary bladder?
A) Squamous
B) Transitional
C) Cuboidal
D) Columnar
Answer: B) Transitional
Explanation: The urinary bladder is lined by transitional epithelium, also known as urothelium. This specialized epithelium can stretch considerably, allowing the bladder to accommodate changes in volume. Superficial umbrella cells help maintain a barrier against urine’s toxic solutes. Squamous epithelium is found in the distal urethra, cuboidal epithelium in kidney tubules, and columnar epithelium in glandular organs. Thus, the correct answer is B. The unique structure of transitional epithelium provides both distensibility and protection, which are essential for bladder function and urinary tract integrity.
2) Transitional epithelium is found in all of the following except–
A) Renal pelvis
B) Ureter
C) Bladder
D) Collecting ducts
Answer: D) Collecting ducts
Explanation: Transitional epithelium lines the renal pelvis, ureters, and urinary bladder. Collecting ducts, however, are lined by simple cuboidal to columnar epithelium, not urothelium. This distinction is important because transitional epithelium must stretch in response to urine storage and transport, a feature unnecessary in collecting ducts. Therefore, D is the correct answer. Recognizing these epithelial differences helps in diagnosing urinary tract disorders and interpreting histopathological slides accurately.
3) A biopsy from a patient with chronic cystitis shows umbrella cells. These cells indicate–
A) Metaplasia
B) Transitional epithelium
C) Keratinizing squamous epithelium
D) Cuboidal epithelium
Answer: B) Transitional epithelium
Explanation: Umbrella cells are the superficial layer of transitional epithelium, characteristic of the bladder. Their presence indicates an intact urothelial lining. Metaplasia would show squamous or glandular changes instead. Keratinizing epithelium is found in skin, not bladder. Cuboidal epithelium lines renal tubules. Thus, B is correct. These dome-shaped cells maintain a barrier and contribute to bladder function, especially during distension.
4) The epithelium most resistant to stretching is–
A) Simple squamous
B) Transitional
C) Simple cuboidal
D) Stratified columnar
Answer: B) Transitional
Explanation: Transitional epithelium is uniquely adapted to withstand distension without losing integrity. Simple squamous and cuboidal epithelia cannot stretch significantly. Stratified columnar epithelium is rare and not adapted for stretch. Therefore, B is correct. The urothelium’s structural specialization helps prevent damage from repeated filling and emptying cycles in the urinary bladder and ureters.
5) A man with long-standing bladder outlet obstruction shows thickened bladder wall. Which epithelial change is most likely?
A) Transitional epithelium hypertrophy
B) Squamous metaplasia
C) Cuboidal proliferation
D) Columnar transformation
Answer: A) Transitional epithelium hypertrophy
Explanation: Chronic bladder outlet obstruction increases intravesical pressure, causing thickening of the bladder wall. The transitional epithelium may undergo hypertrophy but generally remains urothelial. Squamous metaplasia occurs with chronic irritation but is less typical. Cuboidal or columnar changes do not occur in bladder lining. Thus, A is correct, reflecting compensatory epithelial and muscular responses to obstruction.
6) The proximal urethra in males is lined by which epithelium?
A) Transitional
B) Stratified squamous keratinized
C) Simple columnar
D) Cuboidal
Answer: A) Transitional
Explanation: The male proximal urethra is lined by transitional epithelium continuous with the bladder. Stratified squamous appears in the distal urethra, columnar epithelium in parts of the prostatic urethra, and cuboidal in ducts and tubules. Thus, A is correct. This continuity helps maintain a flexible, protective mucosal lining accommodating urine flow and mechanical stress.
7) A child with vesicoureteral reflux may have weakening of which epithelial layer?
A) Columnar
B) Cuboidal
C) Transitional
D) Stratified squamous
Answer: C) Transitional
Explanation: Vesicoureteral reflux involves dysfunction in the ureterovesical junction, lined by transitional epithelium. Weakness in this epithelium or underlying structures predisposes to urine reflux and infections. Squamous, cuboidal, and columnar epithelia are not part of this region. Thus, C is correct. Proper function of urothelium is essential to prevent ascending infections and protect upper urinary tract structures.
8) Urothelial carcinoma arises from which epithelium?
A) Transitional
B) Squamous
C) Columnar
D) Cuboidal
Answer: A) Transitional
Explanation: Urothelial carcinoma, the most common bladder cancer, originates from transitional epithelium. Squamous tumors arise from squamous metaplasia, columnar tumors from glandular metaplasia, and cuboidal epithelium does not give rise to bladder carcinoma. Thus, A is correct. Risk factors include smoking, occupational exposures, and chronic irritation, all affecting the urothelium.
9) In hydronephrosis, the renal pelvis shows dilatation of epithelium normally lined by–
A) Transitional epithelium
B) Simple squamous epithelium
C) Columnar epithelium
D) Pseudostratified epithelium
Answer: A) Transitional epithelium
Explanation: The renal pelvis is lined by transitional epithelium, enabling distensibility. Hydronephrosis causes dilation but the epithelial type remains transitional. Simple squamous lines Bowman’s capsule, columnar lines GI tract, and pseudostratified lines respiratory tract. Thus, A is correct. The urothelium’s stretchability helps accommodate increased pressure but prolonged obstruction leads to damage.
10) Terminal male urethra is lined by–
A) Stratified squamous non-keratinized
B) Transitional epithelium
C) Simple cuboidal epithelium
D) Columnar epithelium
Answer: A) Stratified squamous non-keratinized
Explanation: The distal male urethra transitions to stratified squamous non-keratinized epithelium near the external meatus, suited for protection. Transitional epithelium is proximal, columnar occurs in prostatic urethra, and cuboidal is absent. Thus, A is correct. These changes reflect functional adaptations to urine flow and external exposure.
11) A biopsy shows dome-shaped cells with thickened apical membranes. This finding is typical of–
A) Renal tubules
B) Bladder urothelium
C) Prostate ducts
D) Urethral glands
Answer: B) Bladder urothelium
Explanation: Dome-shaped umbrella cells with thickened apical membranes are characteristic of bladder transitional epithelium. Renal tubules have cuboidal epithelium, prostate ducts columnar epithelium, and urethral glands produce mucus but lack umbrella cells. Thus, B is correct. These surface cells form a protective barrier that adapts to repeated stretch during bladder filling.
Chapter: Embryology; Topic: Development of Urinary System; Subtopic: Derivatives of Urogenital Sinus
Keyword Definitions:
Urogenital Sinus: Endodermal structure forming bladder, female urethra, and lower vagina.
Mesonephric Duct: Gives rise to male reproductive ducts but regresses in females.
Ureteric Bud: Outgrowth forming ureter, pelvis, calyces, and collecting ducts.
Metanephric Blastema: Mesenchyme forming nephrons.
Endoderm-derived Epithelium: Lines bladder and female urethra.
1) Lead Question – 2016
Female urethra develops from–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Metanephric blastema
Answer: A) Urogenital sinus
Explanation: The female urethra arises from the pelvic part of the urogenital sinus, which is derived from endoderm. The mesonephric duct largely regresses in females, forming no part of the urethra. The ureteric bud forms upper urinary tract structures such as ureter and collecting ducts, while the metanephric blastema forms nephrons. Thus, A is correct. Understanding the embryological origin of the urethra is essential in explaining congenital conditions such as urethral anomalies and their association with urogenital sinus maldevelopment.
2) The urinary bladder epithelium is derived from–
A) Endoderm
B) Mesoderm
C) Ectoderm
D) Neural crest
Answer: A) Endoderm
Explanation: The bladder’s lining develops from the endodermal urogenital sinus. Only the trigone region has mesodermal origin due to mesonephric duct incorporation. Ectoderm and neural crest do not contribute to bladder epithelium. Thus, A is correct. This developmental distinction explains transitional epithelium origin and why certain congenital anomalies arise from urogenital sinus defects.
3) A newborn girl presents with urethral atresia. The defect most likely occurred in the–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Cloacal membrane
Answer: A) Urogenital sinus
Explanation: The female urethra forms entirely from the urogenital sinus. Atresia suggests failed canalization or development of this structure. The mesonephric duct regresses in females, the ureteric bud forms upper tract structures, and the cloacal membrane ruptures to form anal and urogenital openings but does not form the urethra itself. Thus, A is correct, linking urethral anomalies to sinus maldevelopment.
4) In males, the prostatic urethra develops from–
A) Mesonephric duct
B) Urogenital sinus
C) Surface ectoderm
D) Cloacal membrane
Answer: B) Urogenital sinus
Explanation: The prostatic urethra arises from the pelvic part of the urogenital sinus in males, similar to the female urethra. Mesonephric ducts contribute ejaculatory ducts, not urethra. Surface ectoderm forms external genitalia. Thus, B is correct. This shared origin explains similarities in epithelial lining and congenital anomalies involving urethral development.
5) The mesonephric duct in females forms–
A) Urethra
B) Gartner duct remnants
C) Bladder trigone
D) Upper vagina
Answer: B) Gartner duct remnants
Explanation: Mesonephric ducts regress in females, leaving Gartner duct remnants along the lateral vaginal wall. They do not form urethra or upper vagina. The trigone is formed by mesonephric duct incorporation but its epithelium becomes endodermal. Thus, B is correct. Gartner duct cysts may arise clinically from these remnants.
6) The ureter develops from the–
A) Urogenital sinus
B) Mesonephric duct
C) Ureteric bud
D) Metanephric blastema
Answer: C) Ureteric bud
Explanation: The ureteric bud gives rise to ureter, renal pelvis, calyces, and collecting ducts. The urogenital sinus forms bladder and urethra. The metanephric blastema forms nephrons. Thus, C is correct. Abnormal budding can lead to duplication anomalies and congenital hydronephrosis.
7) A neonate has bilateral renal agenesis. The defect is most likely in–
A) Ureteric bud
B) Urogenital sinus
C) Cloacal membrane
D) Mesonephric duct regression
Answer: A) Ureteric bud
Explanation: Renal agenesis results from failure of ureteric bud to interact with the metanephric blastema. The urogenital sinus forms bladder and urethra, not kidneys. Cloacal membrane defects affect openings, not kidney formation. Mesonephric duct regression is normal in females. Thus, A is correct. Lack of induction prevents nephron formation, leading to oligohydramnios and Potter sequence.
8) The lower part of the vagina is derived from–
A) Urogenital sinus
B) Paramesonephric ducts
C) Cloacal membrane
D) Mesoderm
Answer: A) Urogenital sinus
Explanation: The lower vagina originates from the sinovaginal bulbs of the urogenital sinus. Upper vagina forms from paramesonephric ducts. Cloacal membrane forms external openings only. Thus, A is correct. Failure of fusion or canalization can cause vaginal atresia or septation.
9) The bladder trigone region is derived from–
A) Mesonephric duct
B) Urogenital sinus
C) Surface ectoderm
D) Ureteric bud
Answer: A) Mesonephric duct
Explanation: The trigone initially forms from mesoderm of the mesonephric ducts but is later overgrown by endodermal epithelium from the urogenital sinus. Ureteric bud forms upper urinary tract, and ectoderm does not contribute. Thus, A is correct. This dual origin explains unique trigonal anatomy.
10) Which structure forms nephrons?
A) Mesonephric duct
B) Ureteric bud
C) Metanephric blastema
D) Urogenital sinus
Answer: C) Metanephric blastema
Explanation: Nephrons—including glomeruli and tubules—develop from metanephric blastema. The ureteric bud forms collecting ducts; mesonephric duct forms male reproductive ducts; urogenital sinus forms bladder and urethra. Thus, C is correct. Proper interaction between blastema and ureteric bud is vital for kidney morphogenesis.
11) A female infant with urogenital sinus malformation may present with–
A) Common opening for urethra and vagina
B) Absent kidney
C) Imperforate anus
D) Enlarged clitoris only
Answer: A) Common opening for urethra and vagina
Explanation: Urogenital sinus anomalies can lead to a persistent common channel for urethra and vagina due to incomplete separation. Kidney agenesis results from ureteric bud defects, not urogenital sinus issues. Imperforate anus involves cloacal membrane. Thus, A is correct. These anomalies often require surgical correction due to functional and developmental concerns.